Until a few years ago fixed temporary dental prostheses were not widely used because, among other things, of their limited life (from a few months to some 1-1.5 years), their relatively high cost and the fact that generally they were intended for a mainly aesthetic purpose.
Recently in the field of dental treatment the real and specific positive functions of fixed temporary prostheses have been increasingly emphasized and reassessed, namely:
their therapeutic function, which among other things permits satisfactory conservation of the tissues and protection of the pulp from the thermal, chemical and bacterial points of view, PA1 the mechanical function, which among other things permits correctly balanced occlusion, restoration of the vertical dimension, correct intercuspation for satisfactory mastication, mandibular glide, compensation for any deformities, and so on, PA1 the aesthetic function, which at the same time results in correct morphology, correct phonology and improved hygiene.
Although fixed temporary and permanent prostheses according to the invention can be provided either as individual prostheses or comprising one or more adjacent teeth, or as two or more prostheses provided on one or both of the dental arches, in the description which follows and in the claims reference will be made to a case with several prostheses for greater clarity. Obviously it is to be understood that the teaching of this invention is independent of the number or type of prostheses produced at any time.
Hereinafter is depicted the known procedure for the production of temporary resin prostheses and permanent prostheses of hard material, or resin, composite resin, ceramic or the like.
The steps in question, substantially and in summary form, are as follows:
1) The dental practitioner (dentist) takes the necessary impressions from the patient, which will subsequently be used by the dental technician (dental mechanic) to prepare the temporary fixed prostheses made of resin.
2) Starting from the impressions received from the dental practitioner, the dental technician produces a model of the upper dental arch and a model of the lower dental arch in plaster (FIG. 1), positions the two models on the articulator (FIG. 2), and finds the correct position for movement and mastication, the occlusion relation and so on of the two models using the records of occlusion provided by the dental practitioner.
3) The dental practitioner and the dental technician study the correct positioning of the models in the articulator and draw the normal clinical conclusions from the points of view of dental treatment and technology.
4) Bearing in mind the general clinical assessments made in step 3), the dental technician relies on his experience and skill in three-dimensional modeling to first obtain the temporary fixed prostheses made of wax. For this purpose the dental technician starts by melting small quantities of wax (as in the so-called drop by drop technique) onto the corresponding model, and more specifically into the hollow areas of the dental arches in which the individual artificial teeth are to be positioned. In this the dental technician proceeds by gradually adding droplets of wax and modeling the individual teeth with a view to completing all the teeth which have to be reconstructed as required from time to time. Fixed temporary prostheses made completely of wax (FIG. 3, seen from above on the mastication side of models with wax teeth in contrasting color; FIG. 4, models with fixed temporary prostheses of wax in the closed position) are obtained in this way. It is obvious that the quality of the shaping of the wax teeth will depend strictly on the personal modeling skill of the dental technician, and in all cases will require extensive modeling time.
5) After the modeling has been carried out and the various parameters which have to be considered have been checked, the dental technician prepares the baseplates, and more specifically one baseplate for each future temporary prosthesis. The baseplates are prepared by applying a mass of plaster or silicone to the wax teeth (FIG. 5).
6) After removing the wax from the model and from the baseplates with jets of hot water, the baseplates and the associated models represent the "negative" of the wax teeth, or a "mold" with cavities (FIG. 6), the shape of which corresponds to the shape of the previously modeled wax teeth, from which the teeth previously made of wax will be obtained in resin. For this purpose the dental technician carries out the so-called "wedging" of the baseplates with resin, or fills the cavities in the baseplates with resin, and then subsequently brings about polymerization of the resin, e.g. by stoving.
7) When polymerization is complete, after the baseplates have been removed from the resin prostheses obtained on the models and these have been positioned in the articulator, the dental technician carries out the steps of checking, rough shaping, finishing and polishing the temporary fixed prostheses. When these operations are complete the temporary prostheses are delivered to the dental practitioner.
8) The dental practitioner places each of the temporary prostheses in the patient's mouth and checks that all functions and predetermined objectives are fulfilled. If this is the case he then fixes the temporary prostheses temporarily using conventional adhesives. If necessary the dental practitioner may make small changes, e.g. by grinding.
It will be seen that the making of teeth by diagnostic modeling in wax constitutes the most difficult and delicate step for the dental technician, who must rely on his skill and mastery as a "sculptor", on the one hand conceiving of the work of sculpting the finished teeth, and then on the other hand putting it into practice by modeling, creating shapes compatible with their corresponding contexts, or guaranteeing optimum mastication. Dental technicians therefore currently need to be well endowed with manual skill and imagination to find and achieve by modeling a proper balance between aesthetic shape, function, optimum mastication and the solution of individual problems. It is obvious that the search for this balance requires both high creative ability--a rare and valuable gift, not always naturally endowed--and a considerable expenditure of time in the daily practice of modeling. This results in quite high costs for the preparation of temporary fixed prostheses.
It will also be noted that once the time specified for use of the temporary prostheses has passed, the final fixed prostheses must be produced in hard material, e.g. resin, composite resin, ceramic, etc., incorporating the corresponding metal or fiber reinforcements. The dental practitioner will again take impressions from the patient's mouth, after having removed the temporary prostheses, so that the dental technician can prepare the permanent fixed prostheses. It is therefore obvious that preparation of the permanent fixed prostheses will be carried out again using the procedure mentioned above. This obviously results in a similar expense in terms of time and cost.